Phonographic apparatus



Aug. 28, 1934.

fiunoonunnnnnuunnnuu G. L. DlMMiCK 1,971,442

PHONOGRAPHIC APPARATUS Filed Feb. 24, 1933 UUDODUDUUUUUDUUUUU Patented Aug. 28, 1934 5 UNITED STATES PHONOGRAPHIC APPARATUS Glenn Leslie Dimmick, Westmont, N. J assignor to Radio Corporation of America, a corporation of Delaware Application February 24, 1933, Serial No. 658,345

11 @laims. (Cl. 274-5) This invention relates to sound or other impulse recording and reproducing apparatus, and

track tend to produce objectionable noise during the reproduction of the recorded sound. To a lesser extent the same result is produced by the *grain of the film upon which the record is made.

Various means of avoiding this difiiculty have been proposed and utilized in the past. Among these ground noise eliminating or noiseless recording means, the best known are the biased light valve utilizedin the recording of variable density sound track, the biased shutter utilized in the recording of variable area sound track and disclosed in United States Patent No. 1,855,197 of Hugh McDowell, Jr., and the biased galvanometer also utilized in the recording of variable area sound track and disclosed in United States Patents No. 1,854,159 of Lewis T. Robinson and No. 1,853,812 of Clarence W. Hewlett.

In all these known systems of noiseless recording, the sound or other impulses to be resystems.

In addition to these indirect recording systems, a limited use has also been made of a direct recording system such as that disclosed by United States Patents Nos. 1,527,649 1,549,550 and 1,598,377 of Charles A. Hoxie. In accordance with this-direct recording system, the acoustic impulses to be recorded are applied directly to a vibratable member or diaphragm and this diaphragm is utilized to modulate the light applied to the light sensitive recording surface which may be or any suitable form such as a moving picture film, a sensitized paper strip, a disk or the like.

While the direct type of recording system has been proposed in various forms and was one of the first to find its way into the art, its use has been negligible due to various difiiculties among which is the problem of operang the direct controlled diaphragm in a manner to eliminate ground noise and permit reproduction or the recorded sound with a high degree of fidelity.

In accordance with the present invention, this difficulty is avoided by the-provision of means whereby a bias pressure dependent on the intensity or volume oi the recorded sound is applied to the diaphragm of the direct recording apparatus. As hereinafter explained, this pressure biasing means may include a chamber formed at the rear of the diaphragm and provided with a valved outlet or with a plurality of small outlets. The invention, however, is not limited to these particular forms but includes other suitable means for applying to the diaphragm a bias pressure which functions to maintain a minimum of light transmitting area on the sound track positive at all intensities of the recorded sound or other impulses.

A ,further object of the invention is to providea sound or other impulse recording system or the .directtype which functions to shift the connection with the accompanying drawing and 35 its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a diagrammatic showing of an impulse recording system to which the invention is applied,

Fig. 2 is an explanatory diagram relating to the character of record produced by the system of Fig. 1,

Fig. 3 is a sectional view of the impulse pickup and diaphragm biasing means which forms a part of the system illustrated by Fig. 1, and

Fig. 4 illustrates a lens mirror or light reflecting element which may form a part of the device of, Fig. 3.

The system of Fig. 1 includes a sound pick-up device 10 provided with a light reflecting element 11 which may. be in the form of a lens mirror (see Fig. 5). Light is applied to this mirror from a source 12 through a lens 13 and an 'apertured light stop 14. The light reflected from the mirror 11 is transmitted through lenses 15 and 16 and alight slit block 17 to alight sensitive recording surface 18 which may be the sound track or a moving picture film 19 or the like (see Fig. 2) With this arrangement, the light applied to the sound truclr lit i "iodulated in accordance with the pressure it es applied to the diaphragm of the pricie -up ice ill. Tithe manner in which this device iunctions will be understood upon examination of Fig. 3.

As indicated by Fig. 3, the pressure impulses to be recorded are applied to a diaphragm so through a mouth piece 21. Atttached to this diaphragm is a drive rod 22 arranged to coop erate with the vibratable support 23 or the mirror 11. It will be observed that this support 23 is pivoted between the drive rod 22 and a sup port 24 mounted at the back of the device ill so that the motion of the diaphragm is transmitted to the mirror.

For the purpose of applying to the diaphragm 20 a bias pressure which is dependent on the intensity of the impulses to be recorded, a menr ber 25 having an opening 26 covered by a resilient cover or flap 27 is provided. It will be observed that a resilient washer 28 of rubber or the like surrounds the driver rod 22 and is attached to the member 25 for the purpose of preventing air leakage around the rod.

With this construction, the pressure in the chamber formed between the diaphragm 20 and the member 25 is dependent on the amplitude of the vibrations to which the diaphragm 20 is subjected. Thus when the amplitude of these vibrations is relatively small, little air is ejected from the chamber through the valve 27 and the bias pressure is low. When the diaphragm vibrates through a relatively large amplitude, 110W: ever, a larger volume of air is ejected through the valve and the biasing pressure is largely due to the fact that air is returned to the chamber at a comparatively low rate. Due to this bias pressure, the zero line about which the diaphragm 20 and the mirror 11 are oscillated is shifted so as to maintain the exposed part or the sound at the maximum value permissible without the peaks of the recorded impulses being cut off by the edge of the record track. Under these conditions, the light transmitting area of the positive sound track is maintained at the minimum permissible value and the ratio of ground noise to signal noise is relatively small.

In the form of the invention illustrated, it is necessary that the bias pressure be negative in value due to the direction of rotation of the mirror and the direction of shift necessary. If, however, the position or either the soundtrack or the mirror support were reversed the direction or bias pressure would have to be also reversed, i. e., made positive, which may be accomplished by reversal of the valve 27. It should be understood, however, that the magnitude and/or variation of the bias pressure may be in either the positive or negative sense in relation to the pressure upon the other side of the dia-- phragm, although for a given set of conditions the direction or sense of the bias pressure remains the same and the pressure varies only in magnitude.

While the invention has been described as applying to the photographic recording 01 sound orother impulses it will be readily understood errace l. The method cl": impulse recording which in eludes subjecting a vibratable member to the inn pulses to be recorded, and applying to said menu bar a bias pressure dependent on the amplitude oi said impulses.

2. The method of impulse recording which in cludcs subjecting a diaphragm to the impulses to be recorded; and applying to said diaphragm a bias pressure which varies in accordance with. the amplitude oi said impulses. 3. The method or sound recording which cludes subjecting a diaphragm to the sound to be recorded, and applying to said diaphragm bias pressure dependent on the volume of said sound.

el. The method of sound recording which in cludes subjecting one side of a diaphragm to the sound to be recorded, andapplying to the op-- posite side of said diaphragm a bias pressure which is dependent on the volume of said sound.

5. The method which includes applying to a vibratable member a pressure which is the resultant of the pressure of the impulses to be re corded and a pressure dependent on the a1nplitude of said impulses, and recording the vibrations of said member.

6. The combination of a diaphragm, means forming at one side of said diaphragm a chamber provided with a valved outlet, and sound recording means operable in response to movement of said diaphragm.

'7. The combination of a diaphragm, means forming at one side of said diaphragm a chamber provided with a valved outlet, and means operable to record the movement of said diaphragm.

8. The combination of a diaphragm, means forming at one side of said diaphragm a charmber provided with a valved outlet, and means operable photographically to record the movement of said diaphragm.

9. The combination of a vibratable member, means forming at one side of said member a chamber from which a fluid is ejected at a comparatively high rate and to which a fluid is admitted at a comparatively low rate, and means operable in accordance with the vibrations of said member.

10. The combination of a vibratable member, means forming at one side of said member a chamber from which a fluid is ejected at a com- -paratively high rate and to which a fluid is admitted at a comparatively low rate, a drive rod connected to said member, and means responsive to the movement of said rod for recording the vibrations of said member.

11. The combination of a vibratable member, means forming at one side of said member a.

chamber from which a fluid is ejected at a comparatively high rate and to which a fluid is admitted at a comparatively low rate, and means including a mirror coupled to said member for photographically recording its movement.

GLENN LESLIE DIM-MICK] 

